Airfoil warping fixture



Feb. 18, 1958 s. o. GOLDSMITH AIRFOIL WARPING FIXTURE 5 Sheets-Sheet 1Filed April. 7, 1955 INV EN TOR. SHAKESPEARE GOLDSMITH ATTORNEY.

Feb. 18, 1958 s. o. GOLDSMITH 2,823,727

AIRFOIL WARPING FIXTURE Filed April 7,, 1955 5 Sheets-Sheet 2 ATTQRNEY',

18, 1958 s. o. GOLDSMITH 2,823,727

AIRFOIL WARPING FIXTURE 5 Shets-Sheet 3 IN VEN TOR.

Filed April '7, 1955 United States Patent This invention relates to awarping fixture and more particularly to a blade warping fixture forblades of the typeas might be used upon the stator of an impeller, orthe rotor of a turbine.

Heretofore in a construction of blades of this type the finallyconstructed blade is formed with a longitudinal twist formed therein ofa predetermined amount.

There has long existed the difficulty of inexpensively and effectivelyforming and warping the initially cast blades or forged blades to acorrect predetermined shape.

It is the object of the present invention to provide a blade warpingfixture which is adapted for attachment to a blade blank and which isadapted to draw the blade through a pair of surface forming rollerswhich operatively engage opposite sides of the blade body as the bladeis drawn therethrough.

It is the object of the present invention to provide a novel ramconstruction by which the said blade is longitudinally drawn through theforming rollers, together with novel mechanism for effecting a rotarymovement of the ram as it is withdrawn longitudinally to thereby impartto the blade a predetermined angular twist along the line of warp pointor center of gravity.

In view of the inherent characteristic of the metal from which theparticular blade is formed and its inherent resiliency, considerationmust be given to effecting a twisting action in excess ,of the finaltwist desired for the reason that there will be a partial returnmovement of the blade towards its original condition.

It is, therefore, the further object of the present invention to providea mechanism whereby the amount of twist of the ram or drawbar may beregulated and accurately controlled.

It is the further object of the present invention to provide a pair ofhydraulically or pneumatically operated rollers which are adapted tocooperatively engage opposite sides of the blade blank and compressivelyengage the same for firmly retaining and guiding the blade as it isdrawn through the said rolls.

It 'is the further object of the present invention to provide a pair ofcomplementary shaped rolls adapted I to engage opposite upright surfacesof the blade and which conform to a predetermined contour orcrosssectional shape in the said blade as it is initially forged or castor otherwise delivered to the warping fixture.

It is the further object of the present invention to provide means forpermitting easy interchanging of rollers depending upon the size andcontour of the particular blade to be warped.

It is the further object of the present invention to provide a centralcontrol mechanism in conjunction with the operation of the hydraulic orpneumatic cylinders for effecting simultaneous inward movement .andcontinuous operative engagement of the said rollers with respect to theblade to be warped, together with means for automatically withdrawingthe said rollers upon release of pressure to thesaid cylinders. 7

These and other objects will be seen from the following specificationand claims in conjunction with the appended drawings, in which:

Fig. 1 is a side .elevational view of a blade blank.

Fig. 1-.A is a section taken on line 1A1A of Fig. 1.

Fig. 2 is a plan view thereof.

Fig. 3 is a diagrammatic indication indicating the intersecting planescorresponding generally to the longitudinal axis of the blade blank ascontrasted with the respective longitudinal axes after the blade warpingoperation.

Fig. 4 is a fragmentary plan view of the present blade warping fixture.

Fig. 5 is a side elevational view thereof, fragmentarily shown, taken online '5--5 of Fig. 4, partially broken away and sectioned forillustration.

Fig. 6 is a left end elevational view taken on line 6-6 of Fig.5,1beinga fragmentary illustration.

Fig. 7 is a fragmentary right end elevational view taken on line 77 ofFig. 4.

Fig. 8 is a fragmentary elevational section of a different form ofbladesecuring adaptor.

Fig. 9 is a side elevational view of one of the movement limitingcollars which are secured to the drawbar in longitudinally spacedrelation.

Fig. 10 .is a fragmentary illustration showing the method of locking theblade securing adapter to theend of the drawbar in exacting relation tocenter of gravity of airfoil.

Fig. 11 is an end elevational view of the adapter shown in Fig. 8.

Fig. 12 is a fragmentary .elevational section illustrating a motor forreciprocating the drawbar.

It will be understood that the above drawings illustrate merely apreferred embodiment of the invention and that other embodiments arecontemplated within the scope of the claims hereafter set forth.

Referring to the drawings, Figs. 1 and 2 illustrate the initially formedairfoil or blade blank prior to the warping operation in the presentwarping fixture.

The said blade consists of an elongated body having opposed upright sidewalls 11 and 12 which are of airfoil configuration which convergetowards their outer end. Said side walls are joined at 14 and form anintegral part of the annular flange 15 at the end of the said bladeblank. Upon the side of said flange opposite from the blade there isprovided a cylindrical hub 16 which has an internal annular recess 17and a central axially extending shank 18, for illustration.

The opposite end of the blade blank terminates in the central axialextension U which provides a means for mounting and supporting thefinally formed air foil or vane or blade within a portion of asupporting element such as the stator body of a compressor or turbine orother type of engine.

Fig. 3 fragmentarily illustrates at 19' the initial longitudinal axis ofthe blade blank, whereas the dotted lines 20 and .21 which centrallyintersect indicate the new intersecting longitudinal axes of therespective twisted portions of the blade body after it has been drawnthrough the present warping fixture.

The said warping fixture hereafter described, with respect to Figs. 4,5, 6 and 7, includes an elongated rectangularly shaped sturdy base 22.At one end of said base and mounted thereon adjacent the oppositemarginal portions thereof are a pair of l-beam supports 23 which arearranged in opposed spaced relation, both supports being illustrated inthe drawing. These supports are immovably anchored to base 22 by thesecuring; bolts 24.

Mounted upon the top surface of each of the said supports 23 arerespectively secured air cylinders 25, both of which are shown in Figs.4 and 7, whose bottom flange U 26 is secured to support 23 as by thefastening bolts 27. These cylinders could be hydraulic.

Compressed air supply pipe 28 fragmentarily illus trated, is joined atone end to the outer end of the cylinder 25 as at 28'.

There is a corresponding conduit 28 indicated in dotted lines in Fig. 4which is adapted to join the opposite outer end of the second aircylinder 25 secured upon the opposite side of base 22 in opposedrelation to the above described cylinder 25. The conduits 28 join the Tfitting 29 which extends from control valve 30 which is suppliedpressure fluid, either liquid or compressed air, through the conduit 31fragmentarily shown, and which valve has a control element 32 wherebyfluid under pressure may be directed to the outer ends of the respectivecylinders 25 as desired for effecting forceful inward movements of therespective pistons 34 within the said cylinders.

Each of the said cylinders has an inwardly directed central guide sleeve33 forming a part thereof through which slidably projects piston rod 36or 52, the latter being joined at its outer end to the piston 34 withincylinder 25.

Coiled spring 35 shown in dotted lines surrounds piston rod 36 and isinterposed between the inner wall of cylinder 25 and said pistonnormally retaining the same in its outermost position. However,referring to Fig. 4, with the rollers 45 and 53 in operative position,actually the pistons 34 would be moved inwardly of the cylinders 25against the action of springs 35. It, therefore, follows that uponrelease of fluid pressure trapped within conduits 28, the said pistons34 in their respective cylinders would be automatically returned to aninoperative or retracted position.

The piston rods 36 are slidably positioned loosely through the uprightsupport 38 which is mounted upon base 22 inwardly of the respectivecylinder with its flange 39 secured by the bolts 40 to the main base 22,as indicated in Fig. 7.

The outer end of piston rod 36 has secured thereto as by a pin or otherstructure the fitting 41 which is threaded as at 42 within and joined tothe recumbent U- shaped or bifurcated roller support or yoke 43.

Roller support 43 has a central upright recess 44 within which ispositioned the upright preformed idler warp roll 45 which is looselyjournaled and supported in an upright position upon the mounting pin 46.This pin extends down through an outer portion of yoke 43, looselythrough roller 45 and with the end of said pin nested within acorresponding recess 48 in the lower portion of yoke 43.

Set screw 47 extends transversely through a portion of yoke 43 and isadapted to anchor the pin 46 in the position shown in Fig. 7.

By this construction with the set screw loosened, the pin may be removedso that different sizes and shapes of warping rolls 45 may be easilyinterchanged for a particular warping job.

The yoke 43 above and below piston rod 36 and spaced therefrom carries apair of horizontally disposed guide bars 49 which are suitably securedto said yoke and which extend rearwardly thereof and slidably throughthe corresponding bushings 50 carried within upright support 38 tothereby provide a more effective and rigid mounting for yoke 43 and tofurther guide yoke 43 and maintain the same in the upright positionshown.

' While the present drawings do not illustrate in detail the secondcylinder 25 which is arranged in opposed relation with respect tocylinder 25 shown in Fig. 4, nevertheless, the present inventioncontemplates this second cylinder as above mentioned, and which hasprojecting therefrom the reciprocal piston rod 52 which carries at itsouter end a second oppositely arranged yoke 51 which is of the sameconstruction as yoke 43 and operates in the same manner under thecontrol of the second cylinder.

' The yoke 51 carries a second upright warp roll 53 which is of a shapecomplemental to the shape and curvature of corresponding wall of theairfoil and is adapted to operatively engage one side of the bladeblank, for example, surface 12 of Fig. 2. It is understood that roll 45would thus engage the opposite side 11 of said blade blank, and is of ashape corresponding to the adjacent wall of said blank.

In normal operation, the amount of pressure to be applied tothe saidrolls depends upon the type of blade to be warped, its construction andthe material from which it is made, and its hardness. Accordingly, it iscontemplated as a part of the present invention that the pressure to beapplied to the piston rods may be varied. For illustration, in a normalwarping operation the pressure applied may be to the extent of 700pounds per square inch, inasmuch as it is necessary during andthroughout the warping operation that equal pressures be applied toopposite sides 11 and 12 of the blade blank as it is drawn through thesaid rolls.

It is contemplated that the cross-sectional shape of the blade blank maybe preformed with the said rolls 45 and 53 serving to operatively engagesuch preformed surfaces during the warping operation.

On the other hand, it is contemplated that the present apparatus mightbe employed for actually forming par tially or fully the cross-sectionalshape of the blade as it is drawn through the rolls 45 and 53.

As shown in Fig. 7, there is provided a second pin 54 of the sameconstruction as pin 46 for loosely supporting and journaling roll 53,and here also this pin is secured in operative position by a set screw47, and upon loosening said set screw may be removed to permit changingof the particular roll 53.

Referring to Figs. 4 and 5, intermediate the ends of the base 22 andcentrally thereof, there is provided an upright standard 55 which issuitably secured to the base as by the bolts 56.

The upper part of said standard carries the support 57 which retains apair of aligned bearing supports or bushings 58 and 59 through whichslidably extends the drawbar 60 which is of generally cylindrical shape,and by which the said blade will be drawn through the said rolls in themanner hereafter described. a

The outer end of said drawbar has an upright trans verse slot 61 formedtherethrough adapted to receive the adapter locating key 62 which issecured by the screw 63 to a portion of drawbar 60 and extendsthere-above. The adapter sleeve 65 loosely extends over the outer end ofdrawbar 60 and has an axial slot 64 therein adapted to cooperativelyreceive key 62 for efiectinga correct registry of said adapter with thedrawbar and to align the transverse apertures in the sleeve with acorresponding aperture in the drawbar for cooperatively receiving thetapered locking pin 66 by which the adapter is immovably secured to thedrawbar.

Said adapter, towards its outer end, has an annular enlarged shoulder 67and in its end face and formed therein a pair of transverse elongatedslots 68 and 69 of rectangular shape in cross-section. Within theseslots are positioned a pair of elongated oppositely arranged clampingfingers 70 which are secured within the said slots by the screws 71which extend into portions of the adapter. Along the inner longitudinaledges of clamp fingers 70 are a pair of oppositely arranged inwardlydirected vane engaging flanges 72 which extend around the flange 15 ofthe blank 1112 for immovably securing the same with respect to theadapter and to thereby assure longitudinal withdrawing movement of thevane with the drawbar 60. It is important in inserting the blank thatits longitudinal axis through the center 'of gravity be in alignmentwith the longitudinal axis of the drawbar, after which it is fixed inposition and retained by clamp fingers 70 or other anchoring means.

Adjustable stop 73 shown in Fig. 9 is secured around a portion ofdrawbar 60 adjacent adaptor 65. Said stop includes a pair of opposedsemi-circularly shaped eleassays? ments 74 and 75 which are securedtogether by the transverse fastening screws 75'. By this constructionthe stop 73 may be longitudinally adjustable upon draw bar 60 andsecured in the desired position thereon. The resilient preferably rubberbumper stop 76 is mounted around draw bar 60 and is retained againstlongitudinal movement by stop 73. This bumper is adapted to cooperatewith the end face of bushing 58 for limiting the withdrawing rearwardmovements of draw bar 60.

A second stop ring 73 is secured to said draw bar adjacent its oppositeend and is adapted to cooperatively engage the end face of bushing 59for limiting return movements of said draw bar. The inner end face ofdraw bar as has an axial bore which is interiorly threaded and isadapted to receive the reduced threaded end 74- of shoulder bolt 10.Said shoulder bolt has a reduced cylindrical portion 77 whichcooperatively extends through the bushing 78 upon the interior of drawbar block 79, there being a pair of thrust washers 7 mounted uponportion 77 of the shoulder bolt cooperatively engaging opposite sides ofdraw bar block 79.

Operating arm 80 is horizontally disposed and at its outer end ispivotally mounted by shoulder screw 80' upon the upper end of theupright support 81 whose bottom flanged base 82 is secured to base 22 asby the bolts 33.

Intermediate the ends of arm 80 there is provided an elongatedtransverse upright slot 84 through which downwardly extends the shoulderscrew 6, with a suitable bushing interposed if desired, said shoulderscrew threadedly engaging drawbar block 79 as at 8.

The operating arm 30 terminates at its outer free end in the operatinghandle 85. By this construction the operating arm may be manuallyactuated in a horizontal plane about its pivot point 80 for effectinglongitudinal reciprocal movements of said drawbar. It is contemplated,however, that power means may be employed for effecting such pivotalmovements of operating arm 80, or for directly moving the drawbar.

Various types of operating arms may be provided such as will effectivelyengage the drawbar block 79 and permit fastening of the operating armthereto for the purpose of producing longitudinal reciprocal movementsof the drawbar.

As shown in Figs. 4 and 5, there is arranged upon base 22 an inclinedcam block 86 which is preferably rectangular in cross-section and whichcarries upon one of its outer upright faces the elongated rectangularlyshaped flat cam face 87 which is secured to the block by the screws 87,Fig. 6.

It is contemplated that the cam face may be angularly adjusted asdesired, with respect to a vertical plane through the drawbar, dependingupon the amount of twist to be made in the blade to be warped. For thispurpose the block 86 is mounted upon the base 22 and secured thereon ina predetermined angular position.

There is also provided in conjunction with the said block suitableclamps of any desired construction which will effectively retain thesaid block in any desired position of angular adjustment.

In the preferred embodiment of the invention there is provided a block90 upon base 22 and which is secured thereon by the fastening screw 91.Elongated clamping strap 92 with central elongated slot 93 is positionedover the upright bolt 94 which is secured to base 22 as at 94, Fig. 5.Said bolt at its upper end extends through slot 93 and has threadedthereover the nut 95 which operatively engages strap 92. One end of saidstrap depends as at 96 for supporting engagement with block 90. The Vopposite depending end 97 of said strap retainingly engages block 86.Consequently, tightening of the nut 95 will effectively secure the camblock in the desired position of adjustment.

Transversely arranged angular reference block 98 is secured upon base 22in any suitable fashion and is 6 adapted for setting the angularity ofblock 86, using a protractor, for illustration, for securing the correctangle. Said rotary control arm 99 shown in Figs. 5 and 6 is bifurcatedat its upper end and is adapted to engage a pair of oppositely arrangedupright slots 101 formed in the surface of drawbar 60 adjacent its oneend, therebeing provided a suitable locking plate for effectivelysecuring the depending control arm 99 rigidly with respect to saiddrawbar and for movement in unison therewith.

The lower end of arm 99 has a ball support 102 with a conical recess1593 therein adapted to cooperatively receive the hardened ball bearing104. Sleeve 105 extends around said ball bearing and has mountedthereover the ball retainer 106 which is bolted to element 102 as by thebolts or screws 107, Fig. 6.

The ball 164 is thus retained upon the lower end of arm d9 and its outersurface projects laterally of retainer 106 for cooperative engagementwith the cam face 87.

As is clear from Fig. 4, upon rotary movement of operating arm 80 by itshandle 85 or by power means in order to effect a withdrawing movement ofdraw bar 6d, the depending arm 99 and its ball 104 will cooperativelyengage said cam plate in such a fashion that during said rearwardmovement the ball will respond to the inclined surface of the cam face87 and thereby effect a predetermined are or rotation upward to the saidarm 99, and accordingly, rotary movement of draw bar 60.

it is contemplated that the amount of twist to be applied to aparticular vane will vary, depending upon the particular stage to whichthe vane is to be applied, and accordingly, the angularity of the flatcam face 87 may be varied asdesired.

In view of the inherent resiliency of the material employed, inoperation it is normally contemplated that the rotary movement will bein excess of the amount desired, inasmuch as the metal will have atendency to return slightly.

Thus there has been provided in conjunction with the present invention adevice whereby a pair of oppositely arranged preformed and mating rollswill operatively engage opposite sides of a preformed vane blank andwill compressively engage the same as the said blade is rearwardlywithdrawn by drawbar 60, utilizing operating arm 80. At the same time,the cam plate 87 through the arm 99 will control the amount of rotarymovement or twist which will be applied to the drawbar and,concurrently, the vane blank as it is drawn through the cooperatingrolls.

The rolls 45 and 53 in a preferred embodiment are constructed of brass,or may be made of any other metal of less hardness than steel.

It is contemplated as an alternative to replacing merely the rolls 45and 53 for different sizes and shapes of blanks that on the other hand,the entire yokes 43 and 51 may be interchanged, or portions of suchyokes.

In Figs. 8 and 11 there is shown a different form of collet or adapterfor securing a blade blank without a flange. The adapter 108 has anaxial bore receiving the end of drawbar 60 and is secured thereto by thetransverse tapered pin 111.

Key 62 secured to bar 60 guidably extends into axial slot 110 in adapter108. The enlarged annular head 112 of the adapter has a bore 113 in itsend face within which are a pair of spring biased blade gripping lugs114 pivotally mounted within bore 113 as at 115.

The inner edges 116 and 117 of the lugs are shaped to correspond to theouter curvature of the leading end of the airfoil blank to therebyprovide an effective means for grippingly engaging an airfoil blank ofthe type which has no securing flange.

It is contemplated furthermore that adapter 108 is interchangeable withadapter 65, or for that matter, any other type of special adapter whichmay be used for a,

specific blade warping operation or for the various stages of bladeswhich may be employed.

Fig. 12 fragmentarily illustrates a different means for reciprocatingbar 60' and employs upon support 55 a cylinder 118 through which drawbar60 slidably and rotatively extends as at points 119.

Piston 120 is secured to bar 60' within cylinder 118 and is responsiveto pressure fluid supplied through either of the pipes 121 or 122 fromthe four-way control valve 123. This valve is joined to a source of pressure fluid or compressed air as indicated at 126. The control valve hasa movable valve element 124 responsive to control 125 for switchingsupply and exhaust connections to the opposite ends of cylinder 118, tothereby provide a motor mechanism for effecting the reciprocal movementsof drawbar 60'.

Having described my invention, reference should now be had to the claimswhich follow for determining the scope thereof.

I claim:

1. A blade warping fixture comprising a horizontal base, a pair ofspaced opposed motors secured upon the base, oppositely arranged alignedpiston rods reciprocally projecting from said motors, yokes upon theouter ends of said piston rods, complementary formed rolls looselyjournaled upon upright axes within said yokes adapted to operatively andcompressively engage opposite side walls of a horizontally disposedupright airfoil blade blank upon energization of the motors, an uprightsupport upon said base, an elongated horizontally disposed draw barslidably and rotatively mounted upon said support extending at rightangles to said piston rods, lying in a general plane intermediate saidrolls and adapted for connection to said airfoil blank, means mountedupon said base connected with said drawbar for longitudinally moving thesame while permitting rotary movement thereof, a control arm rigidlysecured to said drawbar and depending therefrom, an elongated cam platesecured upon said base having a cam face lying in an upright plane at apredetermined angle with respect to and intersecting an upright planepassing through the drawbar axis, the lower end of said control armoperatively engaging said cam face and responsive to lateral thrust toeffect a predetermined rotary movement of said drawbar as it is movedlongitudinally of said cam face, an upright standard secured on the basespaced from said support, said drawbar moving means including ahorizontally disposed arm pivotally mounted at one end upon saidstandard, means upon its other end for effecting horizontal arcuatereciprocal movements thereof, a drawbar journal block loosely mountedupon the adjacent end of said drawbar, and means intermediate the endsof said arm and loosely supported thereby and secured to said drawbarblock whereby the drawbar is free to rotate during longitudinalmovements thereof.

2. A blade warping fixture comprising a horizontal base, a pair ofspaced opposed motors secured upon the base, oppositely arranged alignedpiston rods reciprocally pro ecting from said motors, yokes upon theouter ends of said piston rods, complementary formed rolls looselyournaled upon upright axes within said yokes adapted to operatively andcompressively engage opposite side walls of a horizontally disposedupright airfoil blade blank upon energization of the motors, an uprightsupport upon said base, an elongated horizontally disposed drawbarslidably and rotatively mounted upon said support extending at rightangles to said piston rods, lying in a general plane intermedaite saidrolls and adapted for connection to said airfoil blank, means mountedupon said base connected with said drawbar for longitudinally moving thesame while permitting rotary movement thereof, a controlarm rigidlysecured to said drawbar and depending therefrom, an elongated cam platesecured upon said base having a cam face lying in an upright plane at apredetermined angle with respect to and intersecting an upright planepassing through the drawbar axis, the lower end of said control armoperatively engaging said cam face and responsive to lateral thrust toeffect a predetermined rotary movement of said drawbar as it is movedlongitudinally of said cam face, an upright standard secured on the basespaced from said support, said drawbar moving means including ahorizontally disposed arm pivotally mounted at one end upon saidstandard, means upon its other end for efiecting horizontal arcuatereciprocal movements thereof, a shoulder bolt removably mounted upon theend of the drawbar axially thereof, an apertured drawbar journal blockloosely journaled upon said bolt, said arm having an elongated slottherein intermediate its ends, and a shoulder screw mounted on said armloosely extending through said slot and threaded into said block.

3. A blade warping fixture comprising a horizontal base, a pair ofspaced opposed motors secured upon the base, oppositely arranged alignedpiston rods reciprocally projecting from said motors, yokes upon theouter ends of said piston rods, complementary formed rolls looselyjournaled upon upright axes within said yokes adapted to operatively andcompressively engage opposite side walls of a horizontally disposedupright airfoil blade blank upon energization of the motors, an uprightsupport upon said base, an elongated horizontally disposed drawbarslidably and rotatively mounted upon said support extending at rightangles to said piston rods, lying in a general plane intermediate saidrolls and adapted for connection to said airfoil blank, means mountedupon said base connected with said drawbar for longitudinally moving thesame while permitting rotary movement thereof, a control arm rigidlysecured to said drawbar and depending therefrom, an elongated cam platesecured upon said base having a cam face lying in an upright plane at apredetermined angle with respect to and intersecting at upright planepassing through the drawbar axis, the lower end of said control armoperatively engaging said cam face and responsive to lateral thrust toeffect a predetermined rotary movement of said drawbar as it is movedlongitudinally of said cam face, there being a laterally arranged ballbearing socket at the lower end of said control arm, a ball bearing insaid socket, means loosely retaining said ball bearing, said bearingbeing laterally engageable with said cam face, whereby duringwithdrawing movements of said drawbar, said ball and its arm will beswingably elevated.

4. A blade warping fixture comprising a horizontal. base, a pair ofspaced opposed motors secured upon the base, oppositely arranged alignedpiston rods reciprocally projecting from said motors, yokes upon theouter ends of said piston rods, complementary formed rolls looselyjournaled upon upright axes within said yokes adapted to operatively andcompressively engage opposite side walls of a horizontally disposedupright airfoil blade blank upon energization of the motors, an uprightsupport upon said base, an elongated horizontally disposed drawbarslidably and rotatively mounted upon said support extending at rightangles to said piston rods, lying in a general plane intermediate saidrolls and adapted for connection to said airfoil blank, means mountedupon said base connected With said drawbar for longitudinally moving thesame while permitting rotary movement thereof, a control arm rigidlysecured to said drawbar and depending therefrom, an elongated cam platesecured upon said base having a cam face lying in an upright plane at apredetermined angle with respect to and intersecting an upright planepassing through the drawbar axis, the lower end of said control armoperatively engaging said cam face and responsive to lateral thrust toeffect a predetermined rotary movement of said drawbar as it is movedlongitudinally of said cam face, a laterally arranged ball bearingmounted upon the lower end of said control arm engageable with the saidcam face, said drawbar having a pair of opposed upright slots formedtherein in its outer face, the upper end of said arm having an uprightyoke structure received by said slots for fixedly securing said drawbarand arm together.

References Cited in the file of this patent UNITED STATES PATENTS SmithJune 4, 1872

